Electrical contactor apparatus for guided missiles



a m in an 1 L M m was EFEREWCa fiEA M July 21, 1964 R. F. HERETH 3,141,715

ELECTRICAL CONTACTOR APPARATUS FOR GUIDED MISSILES Filed March 27, 1962 s Sheets-Sheet 1 IN VEN TOR. 1944/ E #676577! GZJL. 'W

ZZZ/V575 July 21, 1964 I R. F. HERETH 3,141,715

ELECTRICAL CONTACTOR APPARATUS FOR GUIDED MISSILES Filed March 27, 1962 3 Sheets-Sheet 2 FIG. 3

FIG. 5

INVENTOR. RALPH F HEEETH QZJAWUWW A TTOE/VEYS United States Patent 3,i4l,715 ELECTRICAL CONTACTQR APPARATUS FOR GUTDED MISMLES Ralph F. Hereth, Port ()rchard, Wash, assignor to the United States of America as represented by the Secretary of the Navy Filed Mar. 27, 1962., $er. No. 133,697 (Ilaims. (Cl. 339-35) (Granted under Title 35, US. Code (1952 see. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to guided missiles and, in particular, to electrical contactors for applying warm-up power to missile components.

Guided missile components, such as signal and powerdrive units, require the usual electrical warm-up which, conventionally, is accomplished by employing an electrical contactor mechanism usually carried by the missile launched in position to electrically engage and impart the warm-up power to the missile immediately prior to its flight.

Structurally, the contactor includes a plurality of pins coupled through suitable leads to a source of electrical power, the pins being carried by a plate that moves into and out of engagement with the missile. The missile itself is constructed with a special electrical connector assembly which is the member that the contactor physically engages. Briefly considered, this connector assembly is formed of a large number of connector elements concentrated in a relatively small area at the skin or surface of the missile. Also, a relatively thin protective plate covers the connectors. In operation the pins of the contactor pierce the connectors protective plate to engage the connector members and to electrically transmit the Warm-up power which is conducted by suitable leads to the particular missile components.

Difiiculties with such contactors arise principally because of their proximity to the intense heat of the missiles blast which, of course, occurs when it is launched. In fact, the heat is so intense that insulation materials, leads, lubricants and other elements deteriorate upon a single short exposure to the blast. Consequently, it is essential either to shield these elements from the blast or to move them entirely out of its way and into a protected position. Exposure obviously is intolerable because launcher operation cannot be disrupted after each firing to replace the contactor. Also, contactors are expensive items.

Adequate protection is difiicult to achieve. For one reason, the contactor must maintain its engagement with the missile until the last possible instant before firing. In one launcher, for example, the allotted time between the actual firing of the missile and the order which initiates the protective movement of the contactor is about .2 of a second. Also, a speed requirement of this nature couples with a need for absolute precision in making and breaking the contactor pin engagement. The pins, of course, must mate precisely with the missiles connectors, and their mating involves both their lateral alignment as well as their axial orientation during the piercing and engaging movements. Other problem areas are present but can be better visualized in conjunction with the detailed description of the contactor and its mode of operation.

It is therefore one of the present objects of the invention to provide an electrical contactor capable of withstanding the deteriorating eifect of a missile blast.

A more specific object is to provide such a contactor 3,141,715 Patented July 21, 1964 in which the deteriorating elements can be protectively shielded from the blasts Within about .2 second from the instant the shielding order is initiated.

Another object is to provide a contactor that can be carried by the missile launcher directly in the path of the blast, the contactor being capable of moving its pins into and out of connector engagement in a straight line motion.

A further object is to coordinate the pin movement of such an electrical contactor with the movement of its pinshielding element so as to reduce the exposure period of the pins to minmium.

Still another object is to provide a self-aligning contactor capable of adjusting its pin positions to correct for minor deviations in the pin orientation.

Another object is to provide a fast-acting fluid pressure drive for simultaneously moving the pins and the pin-shield.

Other objects and their attendant advantages will become apparent in the ensuing detailed description.

The preferred embodiment of the invention is illustrated in the accompanying drawings of which:

FIG. 1 is a rear or tail-end view of a guided missile having an electrical connector adapted to be engaged by the contactor of the present invention;

FIG. 2 is a somewhat schematic side view of a missile launcher illustrating in particular the mounting of the present contactor on the launcher;

FIG. 3 is a side elevation of the contactor showing the opened position of its shield or cover in phantom outline; and

FIG. 4 is a section on lines 4 i of FIG. 3 with wall portions of certain pin chambers broken away to show underlying detail; and

FIG. 5 is a section on lines 55 of FIG. 3.

The particular missile used to illustrate the invention is the Navys so-called Tartar, Mark 11, guided missile, although the principal interest in "this missile is the fact that, as shown in FIGS. 1 and 2 its missile-to-launcher electrical connector section 1 is carried at the rear of the missile directly in the path of its blast 15 which, of course, streams rearwardly of the missile as it is fired or launched. Other missiles may carry their connectors in different positions, but, as long as there is a danger of exposure to the blast, it is essential to provide the protective features to be described.

As shown in FIG. 1, connector 1 is formed of a plurality of electrical connectors 2 bunched together in a trapezoidal configuration and covered protectively by a relatively thin plate 3. Although not illustrated, it will be appreciated that each connector is coupled by an electrical lead to a missile component requiring electrical warm-up power prior to actual flight. Another significant factor is that connector 1 is formed with a pair of guide pin holes 4 and 6; one on each side of the bunched connectors. As will become clearer, holes 4 and 6 receive guide members of the launcher contactor so as to finally align the contactor with the connector.

FIGURE 2 illustrates the manner in which the contactor apparatus of the invention, indicated by numeral 7, is mounted on the particular missile launcher used for firing the Tartar missile. Before considering the launcher, it should be noted that this missile utilizes a semi-active guidance system in which wings 8 and fins 9 may be ground controlled during flight to correct flight path deviations noted by radar illumination coupled with computer techniques. During storage in the missile magazine, fins 9 are folded for space-reduction purposes. Consequently, when a missile is rammed into firing position on its launcher arm 11 it becomes necessary to erect the fins. For this purpose, launcher arm 11 includes a pair of finserecting arms 12 having fingers 13 hydraulically actuated and controlled to engage the fins and move them into their expanded, operative dispositions.

These fin-erector arms are presently significant since, as shown in FIG. 2, contactor 7 is mounted on one of them, preferably the inboard one. Thus, the movement of the erector arms also is utilized to initially position contactor 7 relative to missile connector 1. In a manner not presently significant, the arms are hydraulically swung into and out of operative position, it being necessary to swing the arms outwardly to remove them from the path of the missile as it is being rammed onto launcher arm 11. However, as also shown in FIG. 2, the arms and contactor 7 remain directly in that of its blast 15.

The structural details of contactor 7 are shown in FIGS. 3, 4 and and, as there seen, the contactor can be considered as having several major components including a block housing 20 reciprocably driven by a piston 21 Which, in turn, is mounted in a stationary piston housing 22. A cover 23 protectively encloses block housing 20 and suitable linkage, generally indicated by numeral 24, couples the cover both to movable housing 20 and stationary piston housing 22, so as to swing cover 23 in response to piston reciprocation to and from its solid and phantom line positions of FIG. 3.

Before continuing with the details of these components, it may be noted that the contactor as a unit is provided with a mounting plate 26 by which its stationary housing 22 is bolted directly to fin erector arm 12 of the launcher. Also, electrical power for the contactor is supplied from a junction box 27 (FIG. 3) through a cable 28 coupled into movable housing 20. Hydraulic power for piston 21 is supplied through a transmission line 29 coupled to a pressure source that is not shown. In actual practice, the contactor also requires anti-icing and lubrication systems for which appropriate passages are provided, the anti-icing preferably being accomplished by a glycol circulation. Since these systems are optional refinements, no attempt will be made to specifically identify them.

To facilitate fabrication, assembly and maintenance, certain of the previously-described components have several parts. Thus, stationary piston housing 22 includes a barrel cylinder 31 having a central bore 32 the lower end of the cylinder being closed by an end cap 33 and the cylinder also having a liner sleeve 34 providing the surface on which piston 21 rides. At each side of the cylinder (FIG. 4) are formed integral flanges or bosses 36, which, in a manner to be described, provide journals for securing part of linkage 24. Also, the upper portion of cylinder 31 has a reduced diameter neck portion 37 on which is fitted a bearing ring 38 having a beveled seating surface 39 on which movable block housing 20 normally rests. Since oil or other fluid pressure is admitted into the cylinder, suitable O-rings and other seals are strategically placed.

Piston 21 reciprocates within the cylinder and, as seen, the piston has its lower end extending into end cap 33 where it terminates in a flange detent 41. The piston itself includes a stem or shaft 42 that carries a piston sleeve portion 43 which is uniform throughout most of its length, but provided with an enlargement 44 to ride in cylinder sleeve 34. At its upper end, piston sleeve 43 is threaded to receive a disc-shaped plate 46 that projects radially into a chamber 47, the chamber being an element of movable block housing 20 which will be considered later. Stem 42 of the piston has a knob portion 48 extending through gasket 46, the knob having its upper end formed into an arcuate surface 49, which, as will be described, has functional significance.

To reciprocate piston 21, oil pressure is admitted to its lower end through a port 51 and to its upper end through a port 52, these ports being coupled to hydraulic line 29 and, as will be understood, the hydraulic system includes certain pilot and control valves (not shown) which alternately couple one or the other of these ports to pressure and tank to produce piston reciprocations. Preferably the pilot valve is solenoid actuated under the remote control of a launcher control panel so that piston reciprocation is immediately responsive to a control panel order. Normally, the piston is held in its retracted position by a spring-pressed latch 53 mounted in a latch casing 54 formed integrally with end cap 33. As seen, latch 53 is an elongate dog member slidably mounted in the casing so as to extend into engagement with piston detent 41 or be retracted therefrom. To extend the latch, a spring 56 is mounted in a central bore to bear against the bore at one end and against a closure nut 57 at the other. Latch retraction is accomplished hydraulically by the pressure admitted through port 51 to extend the piston.

With the exception of the piston and its moving parts, the structure described so far is stationary. The remaining structure to be described is for the most part movable either directly or indirectly in response to piston reciprocation. These remaining parts generally include block housing 20, cover 23 and linkage 24.

Block housing 20 also is fabricated from a number of individual parts, principal among which are a block barrel portion 58 having a central bore of graduated diameters to receive a pin block 59, a connection box 61, and a thrust plate 62. Also, the lower end of barrel portion 58 is formed with a beveled interior surface 63 mating with and resting on beveled seat 39 of the piston housing. Immediately above beveled surface 63 (FIG. 4) the central bore of barrel portion 58 has its diameter considerably enlarged to provide the previously-mentioned chamber 47 which receives disc plate 46 of piston 21. It is to be noted that chamber 47 is of greater dimensions than plate 46 to permit the block housing as a whole a freedom of movement relative to the piston and its disc plate.

For purposes of assembly, adjustment and maintenance, it may be noted that barrel portion 58 is, in practice, formed of upper and lower sections 5811 and 58b, chamber 47 being formed in the lower portion. Also, the lower end of upper portion 58a has its external diameter substantially reduced to provide a relatively thin collar portion 64 in which thrust plate 62 is mounted, the collar mounting an adjustable spring pin 66 by means of which its position can be set. A plurality of pins 66 may be employed and adjusted to provide equal radial pressure to center thrust plate 62 and the entire housing with respect to the piston housing. Shims 67 also space thrust plate 62 from a stepped flange of the central bore of barrel 58 to provide additional adjustments.

Another feature relative to block barrel 58 is that its upper end carries a pair of guide pins 68 the function of which has been indicated and will be amplified.

The function of pin block 59 is to mount a plurality of electrical pin connectors 69 which engage and transmit warm-up power to connectors 2 of the missile. Since the pins carry electric current, the walls of the block should be formed of an insulating material or suitable insulation otherwise should be provided. In the illustrated assembly, there are 23 pins each formed with a body having a sharpened end portion projecting upwardly from the pin block to pierce plate 3 of the missile connector. The body portions of the pins are received in openings provided in an upper end wall 71 of the pin block (FIG. 4),-and, interiorly of end wall 71, the pins each are formed with a pair of flanges 72 between which is bound the end of a coil spring 73. Also, the interior of pin block 59 is divided by walls 74 into a number of. separate insulated compartments, one for each pin assembly. Springs 73 extend longitudinally through the compartments to bear at their lower ends on a spring plate 75 which is an integral part of electrical connecting posts 76. As seen, posts 76 project through an upper wall 77 of connection box 61 to provide surfaces within the box onto which electrical leads 70 of supply cable 28 can be bound. Current is transmitted from the posts to the pins. The purpose of springs 73 is to assure equal contact pressure on all pins so that the physical connections between the pins and the missile connectors are equally firm. Of course, the springs must be of sufiicient strength to permit the pins to pierce plate 3 of the missile connector.

The mechanism described so far provides an excellent means for contacting and applying warm-up power to the missile connector. However, as can be appreciated, it would be very short-lived if exposed to the intense heat of the missile blast. To avoid this dilficulty, another feature of the invention is the provision of protective cover 23 to shield the pins and the pin block from the blast, as well as linkage 24 which, in a manner to be described, is responsive to piston reciprocation to expose the pins for engagement with the missile or cover them prior to the blast.

The cover itself is a unitary mechanism sized and shaped to cover the pin-bearing face portion or end wall 71 of the pin block. On the actual launcher this face portion is of substantially the same trapezoidal shape as connector 1 (FIG. 1). Also, as best seen in FIG. 3, end wall 71 of the pin block is canted or beveled so that cover 23 also has its interior face beveled to the same degree. The reason for the bevel will be appreciated upon considering the direction of the swing of the cover from its phantom position (FIG. 3) to its solid line protective position. Thus, as may be noted, the bevel shortens the are through which the cover must swing in its opening and closing movements. Because of the speed at which the blast protection must be provided, this feature is especially beneficial.

The linkage for swing the cover couples the cover to the other members on both sides of the contactor, although the linkages at either side are substantially identical. Specifically each linkage 24 is formed principally of a pair of link arms 78 and 79, link arms 78, however, each being, structurally considered, integral extensions of cover 23. As shown, arms 78 couple the cover to block housing 20, or more specifically, to barrel portion 58b of the housing. Portion 5812, as well as the lower portions of these arms, each is journaled to receive a pivot pin 81 which forms one axis about which the cover swings. Consequently, when the upper housing is moved forwardly or upwardly by its piston, the link coupling of the cover to the housing tends to carry the cover upwardly with the housing in a straight line with it.

Links 79 are used to convert the straight line thrust of the piston on the cover into a swinging movement to open and close the cover. For this purpose, arms '79 are pivotally coupled at their upper end to medial portions of links 78. Also, at their lower ends, links 79 are pivotally secured to boss portions 36 of stationary piston housing 32. The net result is that links 79 restrain any upward movement of the cover and, instead, constrain the cover to swing about the axis of pins 81 of link arms 78.

The coupling for link arms 79 (FIG. 5) is provided by a pair of upper and lower pivot pins 82 and 83 mounted at one end in links 78 and bosses 36 in the customary manner. However, the other ends of these pins, or as shown, the ends received in the upper and lower portions of links 79 are coupled by means of ball and socket joints, the pins having ball portions 84 received in suitable sockets of the links. This ball and socket joint has functional significance to be described later.

Links 79 also are provided with a turnbuckle arrangement for adjustment purposes. More specifically, the links each are forward of an upper and lower half threadably coupled by a bolt 86 having an adjustment nut 87. The opposite ends of the bolt are oppositely threaded to permit the turnbuckle effect which obviously permits a shortening or lengthening of the links as described. As will be noted, these links, as well as other members have various passages for lubricant and glycol. The manner in which such passages are provided is entirely optional.

Other features of the invention can best be understood in conjunction with a description of its intended operation.

As already explained, the first function of the contactor is to quickly expose its electrical connector pins 69 and move them into a warm-up engagement with connector members 2 of the missile connector 1. Upon the initiation of a missile firing order, the contactor must, almost instantaneously, withdraw its pins and move its protective cover over them so as to shield vulnerable parts from the heat of the firing blast.

When an order is received to engage the contactor for warm-up purposes, hydraulic pressure is admitted to port 51 to release latch 53 and simultaneously move piston 21 forwardly. As may be noted, the entire block housing 20 is moved upwardly (FIG. 4) by the piston acting on thrust plate 62, the housing then. moving away from its seated disposition in which its beveled surface 63 rests on stationary seat 39. Cover 23 immediately swings away from its closed position since the forward movement of the block housing carries its pivot pins 81 forwardly so that links 78 must swing a pivot in an arc to maintain their coupled radii. Links 78, of course, must swing because the upper portions of these links are restrained by their fixed coupling to the stationary piston housing through links 79.

In practice the total piston stroke is 1.399 inches minimum and 1.437 inches maximum, so that the cover linkage must swing the cover through its total arc during this short throw. It will be appreciated that contactor 7 has been initially moved into proximity with the missile by fin-erector arm 12 of the launcher.

One feature not previously described is the manner in which contactor pins 69 are aligned with missile connectors 2. Such an alignment is assured by the use of guide pins 68 and also by a so-called floatable engagement of piston 21 with block housing 20. Thus, as may be noted, housing 20 is free to float in all directions once it has been lifted from its resting engagement on piston bevel 39. Specifically, the freedom is permitted by the fact that piston 21 engages the housing only by means of the arcuate surface 49 of its knob portion 48, this knob engaging the under or rearward side of thrust plate 62 which, as shown in FIG. 4, is provided with a conical recess 88 to receive the knob. Recess 88 is a self-centering means functional upon return stroke of the piston.

Also, it is important to again note that disc plate 46 of the piston has a certain amount of play in its chamber 46 and, in practice, the relative dimensions are such that pin block housing 20 can move laterally 7 inch in all directions. The lateral movement is responsive to deviations noted by guide pins 68. Thus, as pin block housing 20 moves forwardly, guide pins 68 first engage guide pin holes 4 and 6 of the missile (FIG. 1) and if the lateral and axial alignment is not perfect, the guide pins and the pin block housing can move laterally a compensating amount. Of course, the guide pins move the housing to align pins 69 of the contactor with the missile connectors 2. The ball and socket jointing of links 79 is functional during this lateral movement. Thus, it will be noted that any lateral movement of housing 20 will carry upper ball joint 84 into an angular or canted position with respect to the lower ball joint. The halls, of course, provide a universal joint which permits a free swinging movement even in this canted disposition.

To retract the pins, hydraulic pressure is applied through port 52. Piston 21, of course, moves downwardly (FIG. 4) or rearwardly carrying its disc plate 46 into contact with lower section 5811 of reciprocal barrel 58 to move section 58b back to its sealed contact with beveled surface 39 of the stationary block housing 22. This rearward movement of the piston is very rapid and the return swing of the cover is equally instantaneous. Also, during the retract stroke, the self-centering engagement of piston knob 48, coupled with the beveled seating of the pin-block housing and with spring pins 66, readjusts the housing to compensate for any lateral displacement that may have occurred. Pins 66, of course, will respond to lateral movement, within the housing so as to have their radial forces unbalanced. At the end of the return stroke, the piston is locked by latch 53 which is snapped into place by spring 56.

It will be appreciated that many of the arrangements specifically described can be accomplished in other manners. For example, although the particular floating and self-centering arrangement has proven most effective and beneficial, it is known that the same purpose can be achieved in other manners. The present advantages stem generally from the rapid straight line movement of the pins being used to flick the cover back and forth. As stated earlier, the cover must close with .2 second from the initiation of a cover-closing order and, of course, some of this time is spent in transmitting the signal. Also, the straight line movement greatly simplifies pin alignment to increase reliability and precision.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. An electrical contactor apparatus for applying warmup power to a guided missile, comprising a contactor block having a front face portion, a swingably-mounted cover protectively enclosing said face, contact pins carried by said face and adapted to engage said missile for applying electrical warm-up power, a piston operatively contacting the block, a stationary piston housing, means for reciprocating said piston to move said block into and out of missile-engaging position, and linkage means said linkage means including a first link arm secured at one end to said cover and pivotally-mounted at its other end portion on said reciprocable contactor block, and a second link arm having one of its end portions engaging said first link arm and its other end portion pivotally mounted on said stationary housing, said second link arm restraining and converting straight-line reciprocal movement of the first link arm into a cover opening and closing swinging movement.

2. The apparatus of claim 1 wherein said reciprocating means is a fluid pressure means, said apparatus further including piston-latching means resiliently urged into piston engagement for holding the piston in said retracted position, said piston housing being arranged to admit fluid pressure to said piston and said latching means for simul taneously advancing the piston and releasing said latch.

3. The apparatus of claim 1 wherein said second link arm is coupled to said first link arm and to said stationary housing by pins, the end portions of the pins engaging said second link arm each being formed as a ball, and said second link arm being formed with sockets receiving said balls, said ball and socket joints permitting said second link arm to adjust in compensation for said block freedom of movement.

4. The apparatus of claim 1 further including selfadjusting centering means for returning said block to its normal orientation with said piston upon a retract stroke of said fluid pressure piston.

5. The apparatus of claim 1 wherein the forward end of said piston fixedly mounts a plate, and said contactor block is formed with a plate-receiving chamber, said piston having a portion projecting through said plate into operative contact with said contactor block, and said chamher being dimensioned in conformity with said plate dimensions for permitting and for limiting said freedom of movement.

6. The apparatus of claim 5 wherein the end portion of the piston projecting through said plate provides the only physical contact between the piston and the block, said contacting piston end portion being formed with an arcuate surface, and said connector block chamber being formed with an arcuate recess receiving said arcuate piston end portion, said arcuate curvatures providing a selfadjusting centering means for returning said block to its normal orientation with said piston upon a retract stroke of said fluid pressure piston.

7. The apparatusof claim 6 wherein said piston housing and said contactor block each are formed with mating beveled seating surfaces.

8. The apparatus of claim 7 further including spring means for adjusting the position of said contactor block relative to said piston.

9. An electrical contactor apparatus for applying warmup power to a guided missile, comprising a contactor block having a front face portion, a swingably-mounted cover protectively enclosing said face, contact pins carried by said face and adapted to engage said missile for applying electrical warm-up power, a piston operatively contacting the block, a stationary piston housing, means for reciprocating said piston to move said block into and out of missile-engaging position, and linkage means, said linkage means including a first link arm secured at one end to said cover and pivotally-mounted at its other end portion on said reciprocable contactor block, and a second link arm having one of its end portions engaging said first link arm and its other end portion pivotally mounted on said stationary housing, said second link arm restraining and converting straight-line reciprocal movement of the first link arm into a cover opening and closing swinging movement, the forward end of said piston fixedly mounting a plate and said contactor block being formed with a platereceiving chamber, said piston having a portion projecting through said plate into contact with said contactor block and said contact being floatable for permitting a limited freedom of movement, said chamber being dimensioned in conformity with said plate dimensions for permitting and for limiting said freedom of movement, and said plate being disposed for engaging a chamber wall upon a retract stroke of said piston whereby said block is moved out of missile engaging position.

10. The apparatus of claim 9 wherein the end portion of the piston projecting through said plate provides the only physical contact between the piston and the block, said contacting piston end portion being formed with an arcuate surface, and said connector block chamber being formed with an arcuate recess receiving said arcuate piston end portion, said arcuate curvatures providing a selfadjusting centering means for returning said block to its normal orientation with said piston upon a retract stroke of said fluid pressure piston.

References Cited in the file of this patent UNITED STATES PATENTS 1,501,157 Woernley July 15, 1924 1,595,862 Doyle Aug. 10, 1926 1,608,732 Farmer Nov. 30, 1926 1,660,180 Van Dorn Feb. 21, 1928 2,438,371 Marholz Mar. 23, 1948 

1. AN ELECTRICAL CONTACTOR APPARATUS FOR APPLYING WARMUP POWER TO A GUIDED MISSILE, COMPRISING A CONTACTOR BLOCK HAVING A FRONT FACE PORTION, A SWINGABLY-MOUNTED COVER PROTECTIVELY ENCLOSING SAID FACE, CONTACT PINS CARRIED BY SAID FACE AND ADAPTED TO ENGAGE SAID MISSILE FOR APPLYING ELECTRICAL WARM-UP POWER, A PISTON OPERATIVELY CONTACTING THE BLOCK, A STATIONARY PISTON HOUSING, MEANS FOR RECIPROCATING SAID PISTON TO MOVE SAID BLOCK INTO AND OUT OF MISSILE-ENGAGING POSITION, AND LINKAGE MEANS SAID LINKAGE MEANS INCLUDING A FIRST LINK ARM SECURED AT ONE END TO SAID COVER AND PIVOTALLY-MOUNTED AT ITS OTHER END PORTION ON SAID RECIPROCABLE CONTACTOR BLOCK, AND A SECOND LINK ARM HAVING ONE OF ITS END PORTIONS ENGAGING SAID FIRST LINK ARM AND ITS OTHER END PORTION PIVOTALLY MOUNTED ON SAID STATIONARY HOUSING, SAID SECOND LINK ARM RESTRAINING AND CONVERTING STRAIGHT-LINE RECIPROCAL MOVEMENT OF THE FIRST LINK ARM INTO A COVER OPENING AND CLOSING SWINGING MOVEMENT. 